1. Field of the Invention
The present invention generally relates to valves, and more particularly concerns pressure regulating valves which are applicable for use at high to very high pressures, such as 1,000 to 10,000 p.s.i.g.
2. Description of the Prior Art
Conventional high pressure spray systems utilize a positive displacement, reciprocating pump and a spray nozzle which has a fixed discharge opening. The desired system pressure is adjusted by controlling flow rate to the nozzle. As the nozzle opening enlarges due to erosion under the influence of the high velocity discharge stream, the flow rate from the pump must be regulated to compensate for the system pressure loss resulting from such wear.
The control of the volume of flow directed to the spray nozzle may be satisfactorily accomplished by providing the pump with a variable speed drive unit. However, variable speed drives are very expensive, especially in the size required to maintain a system pressure of, for example, 10,000 p.s.i.g.
In lieu of a variable speed drive, it is common practice in the spray system field to employ an adjustable pressure regulating valve connected to a valve chamber for bypassing a portion of the discharge flow from the pump. The adjustable valve employs a spring for yieldably biasing the plug thereof against the seat, and the system pressure is controlled by adjusting the tension of the spring. As the spring tension is increased, the flow rate of the bypass flow is decreased, thereby increasing the flow rate from the valve chamber to the spray nozzle and thus the system pressure. As the spray nozzle wears, the associated drop in the system pressure of the valve may be negated by increasing the tension of the spring to thus bypass less flow through the pressure regulating valve.
When operating at very high system pressures, for example, at 10,000 p.s.i.g., the bypass flow is accelerated to very high velocities between the separated mating surfaces of valve plug and valve seat. In known conventional high pressure relief valves, such as disclosed in U.S. Pat. No. 3,087,510 to Normand, the mating surfaces of the seat and plug are tapered annular surfaces which are narrow to insure a fluid-tight seal therebetween. Due to manufacturing tolerances relating to the accuracy of the roundness and taper of the mating surfaces and also to the accuracy of the positioning of the plug in coaxial alignment with seat, the width of the annular surfaces cannot be substantially increased without reducing the effectiveness of the seal. At very high system pressures, even slight misalignment, or roundness, or taper errors can lead to rapid localized erosion of the plug and seat which is ruinous to the pressure regulating characteristics of the valve.
When such erosion occurs in these prior art valves, it is normally necessary to replace both the seat and the plug. Replacement of both is required because the mating surfaces of the two components are customarily lapped together to provide them with the required degree of accuracy of roundness and taper.
Another problem associated with prior known pressure regulating valves used in high pressure systems is the problem of the erosive wear on the parts surrounding the annular exit of the passageway formed between the mating surfaces of the valve seat and plug. Due to the narrowness of the annular passageway, the bypass fluid does not substantially decelerate in the passageway and therefore discharges at very high velocities from the annular exit of the passageway. In the aforementioned tapered plug valve, the bypass flow egresses through an exit bore formed in the valve seat. A cutting stream is produced by egressing liquid which erodes areas of the valve seat bore immediately downstream from the tapered mating surface of valve seat bore, and especially at the side of the bore opposing the main flow of fluid through the valve.
In another sort of pressure regulating valve, the inlet bore is formed through the valve seat and the bypass flow first impinges on the bottom surface of the plug and then flows radially outwardly through an annular passageway between annular mating surfaces of the separated seat and plug. Examples of this general type of valve are shown and described in United States Pat. Nos. 2,568,026 to Pigott; 2,622,613 to McNeal; 2,880,751 to Tobis et al; 2,277,656 to Falls; and 1,949,150 to Eplett. In all of these prior art patents, the seats of the disclosed valves are comparatively narrow. The aforenoted Pigott patent cites a reason for the narrowness of the annular surfaces--to minimize the static pressure exerted by the bypass stream on the plug as the plug begins to separate from the seat and to thus provide more stable operations under various pressure and flow conditions. The narrow annular passageway of each of these prior art valves will not both throttle the bypass stream and reduce under controlled conditions the high velocity of the fluid developed in such narrow passageway; thus, the stream will discharge from the narrow passageway at a high velocity and relatively quickly erode the surrounding parts of the valve.